Routes of Dicyandiamide Uptake in Pasture Plants: A Preliminary Laboratory Study

A consequence of intensification of New Zealand pastures is increased nitrogen (N) inputs to the soil in the form of urine, dung and mineral fertiliser. Dairy cow urine has a high N content that causes large N losses from the grazed system via nitrate (NO3-) leaching, nitrous oxide (N2O) emissions and ammonia volatilization. Dicyandiamide (DCD) is a nitrification inhibitor that has been proven to reduce NO3- leaching and N2O emissions, and increase pasture in New Zealand pastures (De Klein et al., 2014). DCD was commercially available for use in New Zealand pastures until 2013 when its use was suspended due to detection of traces of DCD in exported milk. Although DCD at high doses is relatively non-toxic there is no set maximum residue limit for its consumption. The contamination incident has highlighted the need to understand the pathway by which DCD entered the dairy cow. Nutrients can be absorbed (or taken up) through the leaves via leaf cuticle and stomata of plants (Eichert and Fernández, 2012) and this phenomenon is used to fertilize golf courses and horticultural crops mainly using urea as a spray formulations. Because of the similarity between DCD and urea in terms of molecular weight and structure, we suspected that DCD could similarly be taken up in pasture plants. Few studies have shown the root uptake of DCD but none using pasture plant species. Our objective was therefore to quantify foliar and root uptake of DCD in pasture plants following its application under glasshouse conditions. We hypothesized that DCD can be taken up by both foliar and root uptake pathways